This invention relates to a chair, for example an office chair, having a height-adjustable seat.
DE 43 03 021 A1 discloses an adjustable work chair of this type in which the seat comprises a front part and a back part connected by a transverse hinge and including a first arm connected to the front part of the seat near its front edge and a second arm connected to the back part of the seat. The seat is height-adjustable by means of a lift and can be progressively tilted forwardly from a normal position to an angle of about 15xc2x0. The tilt is such that the entire thigh part of a user""s leg rests on the seat when the lower part of the leg is extends vertically. A standing work position cannot be achieved with this chair.
Ergonomists and occupational health workers have repeatedly commented on the benefits to health of frequent changes from a seated position to a standing position. New work desks offer an adjustment range from seated to standing work positions. Therefore, there is a need for work chairs with an adjustment range between seated and standing work positions. This does not merely involve enlargement of the adjustment range, which would lead to sitting at standing height, as with bar chairs or chairs with a foot ring for stand-up counters. Rather, the standing work position should allow for leaning or short-term crouching to relieve the feet.
EP 0 293 136 B1 and 0 371 729 B1 disclose chairs with seats that are saddle-shaped and that swivel to allow leaning or short-term crouching in the standing position of the seat. A disadvantage here is that a sit/stand position or a seated position on a tilted seat are not possible because of the saddle shape of the seat.
An object of the present invention is to provide an improved adjustable work chair providing sit/stand positions.
In accordance with one aspect of the invention, there is provided a chair having a height-adjustable seat comprising a front seat part and a rear seat part connected by a hinge that extends transversely of the seat. The chair has a lift for raising and lowering the seat and the lift includes a fixed part and a movable part that can be extended upwardly with respect to the fixed part. A first arm is connected between the front part of the seat and the fixed part of the lift, and a second arm is connected between the movable part of the lift and the rear part of the seat.
A work chair of this form is adjustable in the sense of the invention in that it is possible to lift the seat from the normal seated position in such a manner that the front part of the seat is turned through an angle of at least 60xc2x0 from the horizontal. Simultaneously, the back moves up parallel to its original position and a sit/stand or a stand/lean position may be assumed.
A user of the chair may relieve his or her feet by crouching into the rear part of the seat, to which a back rest may be fitted.
Preferably, the seat is divided so that the hinge lies towards the rear of the seat, with the front part forming between a half and two thirds of the overall depth of the seat. A mechanical arrangement allows the front part of the seat to tip downwardly in the upper position. As a result, a shorter seat is presented in the standing or leaning position, as with a high stool. In the sit position, the seat returns to its normal, office chair position and an additional resting position can be attained by tipping the rear part of the seat backwards.
In a first embodiment of the invention, the first arm of the chair is movable both at the front part of the seat and where it joins the movable part of the lift (e.g. the head of an extendable piston). In the second embodiment, the first arm is joined to the front part of the seat so that it is movable but is firmly attached to the fixed part of the lift (e.g. a cylinder receiving the piston). In these two embodiments, the lift may be a gas spring having two individually adjustable lift heights of 190 mm.
The first lift height regulates the seat height between about 400 mm and 590 mm. The second setting regulates the lift from the sit position to the sit/lean position through about 780 mm. Both lifts can be regulated individually so that the second setting is fully expanded in the stand position and the height can be adjusted individually for a small person by means of the first setting. Furthermore, the forward angle of the seat can be regulated individually with the second setting.
In a third embodiment of the invention, the second arm is connected to the back part of the seat at a joint that includes toothed segments. The two arms are coupled together about a common axis defined by an axial spring element such as torsion bar and/or a spring bar at the head of the centre column of the seat support, for the purpose of adjusting the arms with respect to each other. In this embodiment, no lift is necessary. Rather, adjustment of the seat from the seat to the stand position is carried out by simply moving the second arm (attached to the rear part of the seat) upwards, during which the vertical position of the rear part of the seat is maintained by the toothed segments of the joint. At the same time, the front part of the seat can be turned into an almost vertical position about the hinge between the two parts of the seat.
In a further, fourth embodiment, the torsion or spiral spring connects to the top of the centre column by a rack and pinion arrangement which accommodates shifting of weight relative to the centre column of the work chair.
The third and fourth embodiments comprise mechanisms that include a torsion bar and/or spring bar and a static front (first) arm. The third embodiment has a movable rear (second) arm and a centre of gravity that can be adjusted in relation to the torsion bar. The adjustment range of the lift in the seated position is about 260 mm and the lift range in the sit/stand position is about 120 mm. In the fourth embodiment, the torsion bar and/or spiral spring bar is shifted towards the front and up in comparison to the third embodiment, and drives a movable arm that lifts the back part of the seat into the stand/lean position or height. Another spring element (gas-spring or spiral spring) controls synchronized movement of the seat back position in connection with the front torsion bar and/or spiral spring bar and optionally guides the lift mechanism to the stand/lean position. The required adjustment range of the lift in the seated position is about 140 mm to about 160 mm. Lift to the stand/sit position is about 200 mm to 220 mm.